The nervous system is remarkable for its diversity of cell types with estimates suggesting that there are well over a hundred different types of neurons and glial cells. Our ability to understand their distinct functions would be enhanced by the availablity of tools permitting the regulated expression of genes in specific subsets of neural cells. We have produced 2 lines of transgenic mice (the "cholinergic mice") that appear to permit regulated gene expression in neurons that express the neurotransmitter acetylcholine. These mice were generated using a bacterial artificial chromosome (BAC) encoding the choline acetyltransferase gene (ChAT) to drive the expression of the tetracycline transactivator (tTA), which promotes gene expression in the absence of tetracycline. When mated to a distinct transgenic line ("responder mice") containing a candidate gene whose transcription is regulated by the tetracycline operator, the resulting mice should express the candidate gene in cholinergic neurons. In Aim 1, we propose to characterize these lines of cholinergic mice to determine whether inducible gene expression is confined to cholinergic cells and to define conditions for tetracycline-regulated expression. As the use of the cholinergic mouse requires the production of "responder mice", in Aim 2, we propose to test a novel method of producing these lines by first placing the transgene into a BAC, which may help to insulate the transgene from the potentially repressive effects at the sites of insertion into the genome. The cholinergic mouse and the efficient production of responder lines should together create a powerful new tool to better understand the roles played by cholinergic neurons in the brain. This should permit the marking of cholinergic cells with fluorescent proteins, facilitate methods of biasing the production of cholinergic neurons from neural progenitor cells, and help to identify both afferent and efferent synaptic partners through the regulated expression of trans-synaptic molecular tags. Lastly, the cholinergic mouse should lead to an improved understanding of the genes that promote cholinergic synaptic function, which may accelerate the development of therapeutics for the patient with Alzheimer's disease, where the progressive loss of cholinergic neurons plays a pivotal role. Cholinergic neurons, which express the neurotransmitter "acetylcholine", are particularly affected in Alzheimer's disease and drugs that promote their activity have been used to treat this disorder. In order to better understand how cholinergic neurons function, we are proposing to make a versatile animal model that will permit studying the effects of changing the expression of "any gene of choice" in these neurons. By improving our understanding of how these neurons function, we hope to accelerate the development of therapeutics that enhance cholinergic activity and survival, which should benefit the patient with Alzheimer's disease.